1. Field of the Invention
The present invention relates generally to magnetic heads for reading data written to storage media, and more particularly to magnetic read heads for disk drives.
2. Description of the Prior Art
A computer disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head, or heads, which are typically arranged in stacks, read from or write data to concentric data tracks defined on surface of the disks which are also typically arranged in stacks. The heads are included in structures called “sliders” onto which the read/write sensors of the magnetic head are fabricated. The slider flies above the surface of the disks on a thin cushion of air, and the surface of the slider which faces the disks is called an Air Bearing Surface (ABS).
The goal in recent years is to increase the amount of data that can be stored on each hard disk. If data tracks can be made narrower, more tracks will fit on a disk surface, and more data can be stored on a given disk. The width of the tracks depends on the width of the read/write head used, and in recent years, track widths have decreased as the size of read/write heads has become progressively smaller. This decrease in track width has allowed for dramatic increases in the recording density and data storage of disks. Thus, as the track width of recorded information decreases, the width of the read/write heads correspondingly decreases.
The read head track width refers to the width of the read head sensor from the right edge to the left edge, and the stripe height refers to the length dimension from the rear edge to the front edge, which will be part of the Air Bearing Surface (ABS). Both of these dimensions are very important to the operating characteristics of the read head and are very tightly controlled during fabrication. The sensor width and stripe height of read sensors are defined usually by ion milling. In addition the Air Bearing Surface of the slider as a whole, including the front surface of the read sensor, must be lapped to produce the final surface.
During the milling and lapping operations, the magnetic material that makes up certain layers of the sensor typically becomes damaged at any or all of these four edges. As a result, portions of the sensor near these edges may become magnetically inactive. These damaged areas are typically 10 to 100 Angstroms (10-100×10−10 meters). However, as read heads become smaller and smaller in size, these damaged areas become a larger proportion of the overall sensor head area.
Although these damaged areas are magnetically inactive, they are still electrically conductive. They can act as electrical shunts which conduct current which would ideally be channeled through the magnetically active areas which produce the magnetoresistive effect by which the sensor operates.
There are two configurations of read head in common use in the industry today. These are called Current In the Plane (CIP) and Current Perpendicular to the Plane (CPP). A magnetic disk drive having a read head of the CIP configuration 40 is shown in FIG. 4, and discussed in more detail below. For CIP read heads 40, the read sensor 50 is generally sandwiched between two insulation layers, usually designated G1 36 and G2 38 which are made of non-conductive material, to keep the circuit from shorting out. The current flows into and out of the plane of the paper in the pictured figure, through the read sensor 50 rather than vertically, from top to bottom.
In the CPP configuration 42, current flows vertically or from electrical leads positioned above and below the read sensor 50 through the sensor and a read head of this configuration is shown in FIG. 5. In this configuration of read head 42 where Current is Perpendicular to the Plane (CPP), shields S1 30 and S2 34 may also serve a dual function as electrical leads supplying current to the read sensor 50 which lies between them. However, it is also possible to provide separate layers between the shields of high conductivity, non-magnetic material to provide the primary function as electrical leads (not shown). An insulation layer 32 also separates the S1 30 and S2 34 electrical leads in the area behind the read sensor 50, so that they do not short out along their length.
In both CIP and CPP configurations, damage occurs to edge regions of the read sensor during fabrication processes used to produce the final dimensions of the read sensor. These damaged areas are shown in FIGS. 6-7 (prior art), which are top plan views of a read sensor 50 of a magnetic disk drive head 14, with FIG. 6 (prior art) showing a CIP configuration 40 and FIG. 7 (prior art) showing a CPP configuration 42. The read sensor 50 is shown having a front edge 60, rear edge 62, a left side 64 and a right side 66. The dimension between the left side 64 and right side 66 determines the sensor width 68, and is generally established during the sensor-width patterning operation. The distance from the front edge 60 to the rear edge 62 is known as the stripe height 69. The extent of the rear edge 62 is typically established by ion milling during the stripe height patterning operation. The front edge 60 achieves its final dimension and surface finish later when the slider is lapped to define the final ABS.
During certain stages of fabrication of the sensor 50, damaged regions 78 are formed. Thus, the sensor-width patterning produces a left-side damaged region 74 and a right-side damaged region 76; stripe height patterning produces a rear-edge damaged region 72; and front surface lapping produces a front-edge damaged region 70. These damaged regions, 70, 72, 74, and 76 are magnetically inactive, due to disordering of the magnetic materials; but they remain electrically conductive; and can shunt current. Thus, the effectiveness and sensitivity of the read sensor 50 is reduced. These damaged regions are typically in the range of 10 to 100 Angstroms in width.
The CIP configuration 40 is shown in FIG. 6 (prior art), in which the read sensor 50 is flanked by electrical leads 54. Since the current is in the plane, the current moves horizontally, as indicated by the arrow 1. The front damaged region 70 and rear damaged region 72 are shown to shunt current through these regions, as indicated by arrows 3. Current still flows through the main sensor region, and the read sensor 50 can still be expected to function, but its performance is degraded due to the shunting effect of the front damaged region 70 and rear damaged region 72.
The CPP configuration 42 is shown in FIG. 7 (prior art), in which the read sensor 50 is flanked by hard bias material 56. In this configuration, it is common practice to include layers of dielectric insulation 90 between the read sensor 50 and the hard bias material 56 to prevent shunting of the sense current away from the CPP sensor. Since the current is perpendicular to the plane, the current moves into or out of the plane of the paper, as indicated by the circled cross 5. In this configuration, the front damaged region 70, rear damaged region 72, left-side damage region 74 and right-side damage region 76 all shunt current without contributing to the magnetic operation of the sensor 50. Again, current still flows through the main sensor region, and the read sensor 50 can still be expected to function, but its performance is degraded to some degree due to the shunting effect of the front damaged region 70, rear damaged region 72, left-side damage region 74 and a right-side damage region 76.
Thus, there is need for a method and structure which prevent damaged and magnetically inactive areas from acting as shunts which detract from the performance of the magnetically active areas of the read head sensor.